I've got a form in Qt designer that I am trying to promote to a custom widget.
At the moment there is nothing else in the form, so just the QWidget.
When I right click on this widget in the designer, the "Promote to.." option is missing.
I go ahead and select the "Promoted widgets..." option, but then in the resulting
dialog, the "Add" button is grayed out even after I select the custom widget in the top window.

Are you not allowed to promote the top widget to something else?

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